sphinx: Implemented sphinx onion routing

Implements a spec-compliant sphinx onion routing format. The format has
been cross-checked with the go implementation
cdecker/lightning-onion@b9e117e.

daemon/sphinx.h

@@ -0,0 +1,126 @@
+#ifndef LIGHTNING_DAEMON_SPHINX_H
+#define LIGHTNING_DAEMON_SPHINX_H
+
+#include "config.h"
+#include "bitcoin/privkey.h"
+#include "bitcoin/pubkey.h"
+
+#include <ccan/short_types/short_types.h>
+#include <ccan/tal/tal.h>
+#include <secp256k1.h>
+#include <sodium/randombytes.h>
+
+#define SECURITY_PARAMETER 20
+#define NUM_MAX_HOPS 20
+#define HOP_PAYLOAD_SIZE 20
+#define TOTAL_HOP_PAYLOAD_SIZE NUM_MAX_HOPS * HOP_PAYLOAD_SIZE
+#define MESSAGE_SIZE 0
+#define ROUTING_INFO_SIZE 2 * NUM_MAX_HOPS * SECURITY_PARAMETER
+#define TOTAL_PACKET_SIZE 1 + 33 + SECURITY_PARAMETER + ROUTING_INFO_SIZE + \
+	TOTAL_HOP_PAYLOAD_SIZE + MESSAGE_SIZE
+
+struct onionpacket {
+	/* Cleartext information */
+	u8 version;
+	u8 nexthop[20];
+	u8 mac[20];
+	secp256k1_pubkey ephemeralkey;
+
+	/* Encrypted information */
+	u8 routinginfo[ROUTING_INFO_SIZE];
+	u8 hoppayloads[TOTAL_HOP_PAYLOAD_SIZE];
+	u8 payload[MESSAGE_SIZE];
+};
+
+enum route_next_case {
+	ONION_END = 0,
+	ONION_FORWARD = 1,
+};
+
+struct hoppayload {
+	u8 realm;
+	u64 amount;
+	u8 remainder[11];
+};
+
+struct route_step {
+	enum route_next_case nextcase;
+	struct onionpacket *next;
+	u8 *payload;
+	struct hoppayload *hoppayload;
+};
+
+/**
+ * create_onionpacket - Create a new onionpacket that can be routed
+ * over a path of intermediate nodes.
+ *
+ * @ctx: tal context to allocate from
+ * @secpctx: the secp256k1_context for EC operations
+ * @path: public keys of nodes along the path.
+ * @hoppayloads: payloads destined for individual hosts (limited to
+ *    HOP_PAYLOAD_SIZE bytes)
+ * @num_hops: path length in nodes
+ * @sessionkey: 20 byte random session key to derive secrets from
+ * @message: end-to-end payload destined for the final recipient
+ * @messagelen: length of @message
+ */
+struct onionpacket *create_onionpacket(
+	const tal_t * ctx,
+	secp256k1_context * secpctx,
+	struct pubkey path[],
+	struct hoppayload hoppayloads[],
+	const u8 * sessionkey,
+	const u8 * message,
+	const size_t messagelen
+	);
+
+/**
+ * process_onionpacket - process an incoming packet by stripping one
+ * onion layer and return the packet for the next hop.
+ *
+ * @ctx: tal context to allocate from
+ * @secpctx: the secp256k1_context for EC operations
+ * @packet: incoming packet being processed
+ * @hop_privkey: the processing node's private key to decrypt the packet
+ * @hoppayload: the per-hop payload destined for the processing node.
+ */
+struct route_step *process_onionpacket(
+	const tal_t * ctx,
+	secp256k1_context * secpctx,
+	struct onionpacket *packet,
+	struct privkey *hop_privkey
+	);
+
+/**
+ * serialize_onionpacket - Serialize an onionpacket to a buffer.
+ *
+ * @ctx: tal context to allocate from
+ * @secpctx: the secp256k1_context for EC operations
+ * @packet: the packet to serialize
+ */
+u8 *serialize_onionpacket(
+	const tal_t *ctx,
+	const secp256k1_context *secpctx,
+	const struct onionpacket *packet);
+
+/**
+ * parese_onionpacket - Parse an onionpacket from a buffer.
+ *
+ * @ctx: tal context to allocate from
+ * @secpctx: the secp256k1_context for EC operations
+ * @src: buffer to read the packet from
+ * @srclen: length of the @src
+ */
+struct onionpacket *parse_onionpacket(
+	const tal_t *ctx,
+	const secp256k1_context *secpctx,
+	const void *src,
+	const size_t srclen
+	);
+
+void pubkey_hash160(
+	const secp256k1_context *secpctx,
+	u8 *dst,
+	const struct pubkey *pubkey);
+
+#endif /* LIGHTNING_DAEMON_SPHINX_H */